Mechanical clutch assemblies are customarily employed between rotatable drive and driven members to establish selective engagement between the members when torque is applied to the drive member. A typical application is in four-wheel drive controls for vehicles so as to permit selective engagement and disengagement of the drive axle with respect to the front wheels in converting between a two-wheel drive and four-wheel drive. In the past, numerous clutch mechanisms have been devised for this and other applications but have relied to a great extent upon a biasing spring force to slidably disengage two intermeshed gears while sliding one of the gears along a drive shaft. The adhesion of the interfaced gears and of the sliding gear to the drive shaft which is caused by parasitic or latent torque, surface conditions of the intermeshed parts, lubrication or the lack of same, temperature, dirt, clearances, grease viscosity, parts concentricity, burrs, contamination and other conditions have under certain conditions interfered with the disengagement of the teeth between the intermeshed gears so as to result in serious malfunctioning. In any event, clutch mechanisms which rely upon a spring or springs to cause quick disengagement between intermeshing gears are functionally limited by the environmental conditions within the mechanism. Moreover, the return springs in order to possess sufficient force to cause disengagement often impose thrust loads upon the axial thrust bearings of the vehicle as well as bearings supporting the actuating members so that allowable return spring pressures are limited by the construction and parts presently employed in vehicular wheel designs.
One principal problem affecting proper functioning of a clutch mechanism of the type described is that of lubricant conditions and specifications. Extreme hot or cold temperatures will cause standard lubricants to congeal or nearly solidify. Moreover, once a vehicle is in the hands of an owner there is no assurance that the proper lubricants will be employed. Another problem occurs when the vehicle wheels are turned before or during the attempt to disengage the clutch mechanism to impart a substantial cocking pressure to the interfaced gears and the interface between the axle spline and gear thereby requiring increased force to disengage the parts.
Another requirement for four wheel drive vehicles is for all four wheels to remain engaged with the power train even during a steep or sudden descent. It is therefore desirable to provide a clutch mechanism which is capable of positive engagement and disengagement under the control of the vehicle operator without being affected by the aforestated and other known environmental or operating conditions and further will not impose unduly heavy loads on any of the thrust bearings employed within the clutch mechanism or vehicle.
Representative patents which disclose clutch mechanisms for four wheel drives are my U.S. Pat. No. 3,217,845; 3,442,361 to Hegar; and 3,656,598 to Goble. Examples of ball and cam arrangements employed in a clutch mechanism to obtain axial movement in response to the application of torque is shown in U.S. Pat. No. 3,829,147.